This invention relates to wire cut electric discharge machines. More particularly, the invention concerns a wire cut electric discharge machine in which a tapering operation is carried out by moving the wire guide horizontally which tensions the wire electrode.
FIG. 1 is a schematic diagram outlining a tapering operation accomplished by an ordinary wire cut electric discharge machine. In FIG. 1, reference numeral 1 designates a wire electrode; 2, an upper wire guide; 3, a lower wire guide; 4, a workpiece to be taper-machined; and 5, a reference table on which the workpiece 4 is placed.
In the case where, with the wire electrode 1 inclined at a specified angle, a tapering machining is carried out by the wire cut electric discharge machine thus constructed, the upper wire guide 2 is spaced as much as a distance e from a vertical line 6 which passes through the lower wire guide 3 and is normal to a top surface of the reference table 5, so that a wire electrode 1 forms a taper angle .theta. with the vertical line 6.
On the other hand, in the case where the workpiece 4 having a thickness t is tapered at an angle .theta., it is necessary to space the upper wire guide 2 a distance X from the reference table 5, and to space the lower wire guide 3 a distance Y from the reference table 5.
A method of calculating the distances X and Y to obtain the taper angle .theta. will be described with reference to FIG. 2 and FIGS. 3(a) and 3(b).
FIG. 2 is a schematic diagram showing a side view of a jig for calculating the distances X and Y. In FIG. 2, reference numeral 7 designates a jig; 8, an upper detecting part; 9, a lower detecting part and character a denote the height of the lower detecting part 9 from the reference table; and b, the height of the upper detecting part 8 from the same.
FIGS. 3(a) and 3(b) are explanatory diagrams for calculation of the distances X and Y.
In FIGS. 3(a) and 3(b), reference character 2a designates the position of the upper wire guide 2 set when the wire electrode 1 is brought into contact with the upper and lower detecting parts 8 and 9 of the jig 7; 3a, the position of the lower wire guide 3 set when the wire electrode 1 is brought into contact with the upper and lower detecting parts 8 and 9 of the jig 7; 2b and 3b, the positions of the upper and lower wire guides 2 and 3 set when the wire electrode 1 is turned clockwise by a taper angle .theta..sub.a and the wire electrode is maintained contacting with the lower detecting part 9; e, the distance for which the upper wire guide 2 has been moved to turn the wire electrode by the taper angle .theta..sub.a ; c, the distance between the positions 3a and 3b of the lower wire guide 3; 2c and 3c, the positions of the upper and lower wire guides 2 and 3 set when the wire electrode 1 is inclined counterclockwise at the taper angle .theta..sub.a and the wire electrode 1 is kept contacting with the upper detecting part 8; and e, the distance for which the upper wire guide has been moved to incline the wire electrode 1 as described above; d, the distance between the positions 3a and 3c of the lower wire guide 3; and z, the reference height of the upper wire guide 2 in the Z- axis direction.
Now, a procedure of automatically calculating the distances X and Y of the upper and lower wire guides 2 and 3 from the reference table 5 will be described with reference to FIG. 4 showing a flow chart therefor.
After parameters necessary for calculation such as the taper angle .theta..sub.a and a tolerance for the taper angle have been inputted, a program as shown in FIG. 4 is executed. First, in Step S1, as shown in FIGS. 3(a) and 3(b), the wire electrode 1 is held vertical and brought into contact with the upper and lower detecting parts 8 and 9; that is, the wire electrode 1 is positioned in place. More specifically, the positions of the upper and lower wire guides 2 and 3 are as indicated at 2a and 3a. Thereafter, in Step S2, the coordinates of the positions of the upper and lower detecting parts 8 and 9 are stored in a memory (not shown).
In Step S3, as shown in FIG. 3(b), the upper wire guide 2 is moved by the distance e horizontally so that the wire electrode 1 is inclined clockwise at the specified angle .theta.a; and in Step S4 the wire electrode 1 is brought into contact with the lower detecting part 9. As a result, the positions of the upper and lower wire guides 2 and 3 are as indicated at 2b and 3b, respectively. In Step S5, the distance c between the positions 3a and 3b of the lower wire guide is stored in the memory.
In Step S6, as shown in FIG. 3(b), the upper and lower wire guides (2a and 3a) holding the wire electrode is vertical is moved horizontally, so that the wire electrode 1 is inclined counterclockwise at the specified angle .theta..sub.a, 6.degree. for instance. In Step S7, the wire electrode 1 is brought into contact with the upper detecting part 8. As a result, the positions of the upper and lower wire guides are as indicated at 2c and 3c. In Step S8, the distance d between the positions 3a and 3c of the lower wire guide is stored in the memory. In Step S9, the data stored in the memory, and the input parameters are utilized to calculate the data required for control of the movement of the wire guides; that is, the distance X.sub.b between the reference table 5 and the upper wire guide 2, the distance Y.sub.b between the surface table 5 and the lower wire guide, and the taper angle .theta..sub.b as follows: ##EQU1##
In Step S10, it is determined whether or not the difference between the data .theta..sub.b obtained from equation (3) and the specified angle .theta..sub.a is within a predetermined tolerance .theta..sub.c. If it is within the tolerance, then Step S11 is effected; that is, the data X.sub.b, Y.sub.b nd .theta..sub.b thus calculated are stored in the memory, and the data X.sub.b and Y.sub.b are used to move the wire guide. If (.theta..sub.b -.theta..sub.a) is more than the tolerance .theta..sub.c, then Step S3 is effected again, and the following Steps are carried out.
In the above-described conventional wire cut electric discharge machine, an error in manufacturing the jig 7 adversely affects the distance X between the reference table and the upper wire guide and the distance Y between the reference table and the lower wire guide, as a result of which accuracy in the taper-machining is degraded. Further, discharge reaction force generated during machining, resistance in the flow of a machining solution and the like may result in an occurrence of deformation of a wire electrode during the machining. The deformation and the difference in thickness of a workpiece cause an error to occur during an actual machining operation.
Accordingly, an object of the present invention is to eliminate the above-described difficulty accompanying a conventional wire cut electric discharge machine. More specifically, an object of the invention is to provide a wire cut electric discharge machine which can perform a tapermachining with high accuracy even if the jig has a manufacture error and there occurs an error in an actual machining.
A wire cut electric discharge machine according to the invention comprises: automatic calculating means for calculating with a special purpose jig the distances of the upper and lower wire guides from a surface table which are necessary for moving the wire guides to incline the wire electrode through a predetermined angle; correction factor calculating means for calculating a correction factor for the distances of the upper and lower wire guides from the surface table according to a difference angle between the predetermined and the taper angle of a workpiece which has been machined for test with the predetermined angle; and automatic correcting means for correcting the distances of the upper and lower wire guides from the surface table by multiplying the distances by the correction factor thus calculated.
In the wire cut electric discharge machine of the invention, the correction factor calculating means calculates the correction factor which is to correct the error attributing to the special purpose jig, according to the difference between the predetermined angle and the taper angle of a test workpiece which has been machined with the predetermined angle, and the automatic correcting means uses the correction factor to correct the distances of the upper and lower wire guides from the surface table, which have been calculated as necessary for controlling the movement of the wire guides.
That is, the wire cut electric discharge machine of the invention is markedly improved in tapering accuracy.